Each choir director at some point in his career (hopefully very early on) will form in his head an ideal sound for his choir (just because you have an ideal sound, doesn’t mean your choir will sing the same way for Palestrina as it does for Brahms and it doesn’t mean that this sound won’t chance throughout your career).  I have found it beneficial to listen to the great choirs of the world as I continually strive to find my ideal.  One of the great places to hear great music is on BBC Radio 3 (http://www.bbc.co.uk/programmes/b006tp7r) every Wednesday during their weekly broadcast of Choral Evensong (or when the Catholic choirs in England sing, Choral Vespers).  Today is a great day to start since the Men and Boys of St. Paul’s Cathedral, London, are in the docket.  Have fun while you are listening and visit the cathdral’s website, specifically the music page(https://www.stpauls.co.uk/worship-music/music/choir-musicians), and see if there isn’t anything there for you and your choir!